- Boilers
- Gas boiler
F7
Junkers F7 on a gas boiler: flame detected with the appliance off
Risk level
High
Professional inspection is recommended.
Urgency
High
Quick answer
Junkers F7 means the boiler sees a flame when it should be off. Press reset once as Bosch describes; if F7 returns, leave the boiler off and call the service centre. If you smell gas, leave and call from outside.
Safety first
Stop and check this first
- If you smell gas: close the gas shut-off valve, open the windows, do not operate switches, put out any flame and, from outside the home, call the gas company and an authorised installer. If you smell flue gases: switch the boiler off, open doors and windows and call the installer.
- Do not chain resets with F7: if it returns after one reset, leave the boiler off. Do not open the casing or touch electrodes, board or flue duct.
Safe checks you can perform
- Gas or flue gas smell before touching anything
- One reset with the reset key
- Visible damp in the boiler room
- Electrode, board and flue check by the technician
Leave these tasks to a qualified professional
- Do not attempt this professional task: Ionisation current reading with the burner off
- Do not attempt this professional task: Board and flue duct check
- Do not attempt this professional task: Function test and combustion analysis
What a technician must be able to justify
Technician visit
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Ionisation current reading with the burner off
What they doThe technician checks the flame signal the board sees with the burner stopped and inspects the ionisation electrode and its cable.
They must show youthe flame reading with the burner stopped and the electrode inspected.
In writingwhether the electrode or cable was replaced and why.
Board and flue duct check
What they doThe technician confirms the board is not damp and the flue duct is in good condition.
They must show youthe board and duct inspected.
In writingwhat was found and what was repaired.
Function test and combustion analysis
What they doAfter the repair, the technician starts the boiler, measures CO2 or O2 with an analyser and confirms F7 does not return.
They must show youthe analyser printout and the boiler running without F7.
In writingthe values recorded in the service log.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Follow these steps
Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
Gas or flue gas smell before touching anything
- Who:
- you.
- How:
- go into the boiler room and notice whether it smells of gas or burnt gases. Do not open the boiler.
- Result that matters:
- whether there is a smell.
- If it smells of gas or fumes:
- do not reset; follow the gas warning on this page.
- If there is no smell:
- you can move on to the reset.
- Evidence to keep:
- note the time and whether there was a smell.
Evidence: Junkers Cerapur Excellence Compact, instrucciones de uso de la caldera mural a gas de condensación · Junkers ZWE 24-3 y 28-3 H A con Bosch Heatronic, instrucciones de instalación
One reset with the reset key
- Who:
- you.
- How:
- press reset as Bosch describes to unlock the boiler, once only.
- Result that matters:
- whether the boiler runs again or F7 comes back.
- If it runs and F7 does not return:
- note the date; it may have been a one off signal.
- If F7 returns:
- Bosch explains some faults cannot be cleared with a reset; leave the boiler off and call the service centre.
- Evidence to keep:
- a photo of the display with F7 and the three digit number shown below it.
Evidence: Junkers Cerapur Excellence Compact, instrucciones de uso de la caldera mural a gas de condensación
Visible damp in the boiler room
- Who:
- you.
- How:
- without opening the boiler, look for leaks, steam or condensation on the casing or the wall.
- Result that matters:
- whether the boiler may have got wet.
- If there is damp or dripping:
- tell the technician; Bosch lists a damp board as a cause.
- If everything is dry:
- damp becomes a weaker explanation.
- Evidence to keep:
- photos of the area and any leak.
Evidence: Junkers CerapurComfort ZWBC 25-2 C, instrucciones de instalación y manejo para el técnico
Electrode, board and flue check by the technician
- Who:
- authorised gas technician.
- How:
- opens the boiler and checks electrodes and cables, damp on the board and the flue duct.
- Result that matters:
- which of Bosch's checks fails.
- If the electrode or its cable is damaged:
- that confirms the cause.
- If they are fine and the board was damp or the flue is at fault:
- the cause is there.
- Evidence to keep:
- a report of what was checked and any part replaced.
Opening the boiler and touching electrodes or the flue duct is work for an authorised gas technician only.
Evidence: Junkers CerapurComfort ZWBC 25-2 C, instrucciones de instalación y manejo para el técnico · Junkers ZWE 24-3 y 28-3 H A con Bosch Heatronic, instrucciones de instalación
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- Boilers
- Brand
- Junkers
- Product type
- Gas boiler
Known code variants
- Cerapur F7
- DishDrawer F7
- error F7 DishDrawer
- Error F7 Junkers
- F 7
- Fisher & Paykel DishDrawer F7
- Fisher Paykel F7
- Junkers F 7
What it means
In the CerapurComfort fault table, F7 means the appliance sees a flame even though it is off; on the ZWE with Heatronic it is a wrong ionisation signal. The board monitors the ionisation current through the electrode. Bosch says to check the electrodes and their cable, the flue duct and that the circuit board is not damp. The code says the signal does not add up, not which of those parts has failed.
Warnings and stop conditions
- Criticalsource verified
If you smell gas: close the gas shut-off valve, open the windows, do not operate switches, put out any flame and, from outside the home, call the gas company and an authorised installer. If you smell flue gases: switch the boiler off, open doors and windows and call the installer.
Evidence: Junkers Cerapur Excellence Compact, instrucciones de uso de la caldera mural a gas de condensación · Junkers ZWE 24-3 y 28-3 H A con Bosch Heatronic, instrucciones de instalación
- Highsource verified
Do not chain resets with F7: if it returns after one reset, leave the boiler off. Do not open the casing or touch electrodes, board or flue duct.
Evidence: Junkers CerapurComfort ZWBC 25-2 C, instrucciones de instalación y manejo para el técnico · Junkers Cerapur Excellence Compact, instrucciones de uso de la caldera mural a gas de condensación
Symptoms and causes
Probable causes · in order
- Damaged ionisation electrode or cablePossible
Bosch says to check whether the ionisation electrode or its cable is damaged. That gives a flame signal with no real flame; only visible with the boiler open.
Evidence: Junkers CerapurComfort ZWBC 25-2 C, instrucciones de instalación y manejo para el técnico · Junkers ZWE 24-3 y 28-3 H A con Bosch Heatronic, instrucciones de instalación
- Damp circuit boardPossible
The CerapurComfort asks to check the board is not damp. If F7 shows up after damp or condensation in the room, this is more likely than the electrode.
Evidence: Junkers CerapurComfort ZWBC 25-2 C, instrucciones de instalación y manejo para el técnico
- Flue duct problemPossible
Bosch includes checking the flue duct is sound. It stands apart because the technician finds the duct damaged or flue gas returning, not an electrical fault.
Evidence: Junkers CerapurComfort ZWBC 25-2 C, instrucciones de instalación y manejo para el técnico
Virtual technician
Does F7 still appear after these checks?
Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.
Sources and technical references
- 1
Junkers CerapurComfort ZWBC 25-2 C, instrucciones de instalación y manejo para el técnico
Junkers (Bosch Termotecnia) · 2012 · manual
- 2
Junkers Cerapur Excellence Compact, instrucciones de uso de la caldera mural a gas de condensación
Junkers (Bosch Termotecnia) · 2019 · manual
- 3
Junkers ZWE 24-3 y 28-3 H A con Bosch Heatronic, instrucciones de instalación
Junkers (Bosch Termotecnia) · 2000 · manual
Was this entry useful?